Sadly unless you are a paid up member of the fun forum you cannot download the PDF document your link refers to, (I'm not).
I have just read through the entire post that the link above opens but other than lots of reference to existing membership there is nothing regarding new membership.
So will believe the email I received from the company the content of which was in my original post.
ADAC stopped accepting new members who have a non-German home address during 2019 (or maybe 201
. Think that's what their initial response to you is predicated upon?
Existing members based outwith Germany are permitted to renew (just did mine earlier this month) and retain existing terms and conditions.